The present invention relates to a photointerrupter used or detecting a desired object or desired part of an object. It also relates to a case used for such a photointerrupter.
A typical prior art photointerrupter, which is disclosed in JP-U-6-50365 for example, has such a structure as shown in FIGS. 12 and 13 of the accompanying drawings. The illustrated photointerrupter B comprises an LED lamp 7, a photodetector 8 and a case 9. The LED lamp 7 as a light emitting element comprises an LED chip 70 sealed in a transparent resin 71. The LED lamp has two leads 72. The photodetector 8 comprises a light receiving element sealed in a transparent resin 81. The photodetector has two leads 82. The case 9 includes a pair of receiving portions 90 for receiving the LED lamp 7 and the photodetector 8, respectively, and a plurality of walls for defining the receiving portions.
Each of the receiving portions 90 has an opening 91 at the bottom. The plurality of walls include a pair of opposite walls 92A each of which is formed with a slit 94 for allowing light emitted from the LED lamp 7 to travel toward the photodetector 8. When an object to be detected (not shown) exists between the slits 94, the object blocks light from the LED lamp 7. As a result, light cannot be received by the photodetector 8 so that signal output from the two leads 82 stops. In this way, the presence or absence of an object is checked.
The case 9 further includes another pair of walls 92B each of which is formed with a projection 95 having an increasing thickness toward its upper end. The upper end of each projection 95 partially extends into the corresponding receiving portion 90. With this structure, the upper end of each projection 95 is brought into engagement with the resin 71 of the LED lamp 7 or the resin 81 of the photodetector 8, thereby fixing the LED lamp 7 or the photodetector 8 in the corresponding receiving portion 90. In the photointerrupter B, therefore, the LED lamp 7 and the photodetector 8 need not be press-fitted into the receiving portions 90, so that deformation of the LED lamp 7 and the photodetector 8 due to such press fit can be avoided. Moreover, since a lid which is separate from the case 9 need not be provided to fix the LED lamp and the photodetector 8, it is possible to reduce the number of parts of the photointerrupter.
However, the above-described prior art apparatus has the following problems.
In the prior art apparatus, the slits 94 for light transmission are provided in the walls 92A of the case 9, whereas the projections 95 are provided in the walls 92B which are separate from the walls 92A. Therefore, in forming the case 9 by resin molding, large openings 99 for forming the projections 95 are provided in the walls 92B. Specifically, as shown in FIG. 14, when the case 9 is formed by using a mold 4C comprising an upper mold member 48 and a lower mold member 49, portions 48a of the upper mold member 48 need to be disposed above clearances 95xe2x80x2 for forming the projections 95 in the case 9. As is clear from the configuration of the projections 95 shown in FIG. 12, part of the upper mold member 48 needs to extend on both sides of the corresponding clearance 95xe2x80x2 for forming the projection 95. Accordingly, the case is correspondingly formed with openings 99.
Since each of the walls 92B of the case 9 is formed with an opening 99, disturbing external light is likely to enter the corresponding receiving portion 90 at the opening 99. In the prior art apparatus, therefore, disturbing external light is received by the photodetectors 8, which leads to malfunction of the apparatus.
It is an object of the present invention to provide a photointerrupter and a case for a photointerrupter which are capable of eliminating or reducing the problems of the above-described prior art apparatus.
In accordance with a first aspect of the present invention, there is provided a photointerrupter comprising a light source, a photodetector, and a case. The case includes a pair of receiving portions each of which is open at one end for receiving the light source or the photodetector, and a plurality of walls defining the pair of receiving portions. The plurality of walls of the case include a pair of first walls each of which is formed with a respective elongated slit. The case further includes a pair of projections each of which projects into a respective one of the receiving portions for preventing the light source or the photodetector from coming out of the receiving portion. Each projection is connected to a respective one of the first walls on an extension line of the respective slit.
Preferably, each projection may be connected to a longitudinal end edge of the respective slit.
Preferably, the case may be made of a synthetic resin, and the pair of projections may be integral with the plurality of walls.
Preferably, each projection may include a base end connected to the respective first wall and a tip end projecting into the respective receiving portion for engagement with one of the light source and the photodetector.
Thus, according to the present invention, in forming the case of the photointerrupter by resin-molding using a mold, part of the mold for forming the slit can be utilized for forming the projection. Therefore, unlike the prior art apparatus, the case of the present invention is not formed with a large opening at portions other than the first walls at which the slits are formed. Therefore, disturbing external light is less likely to enter the receiving portions, which enhances reliability of detection by the photointerrupter.
Preferably, each projection may be elastically deformable for allowing movement of the tip end toward the respective first wall.
With this structure, each of the light source and the photodetector can be easily inserted into the corresponding receiving portion by pushing the tip end of the corresponding projection by the light source or the photodetector toward the corresponding first wall. After the light source and the photodetector are inserted into the respective receiving portions, the tip end of each projection projects into the corresponding receiving portion due to the elastic recovery. Thus, fixing of the light source and the photodetector can also be performed easily.
Preferably, a rounded connection may be provided between the base end of each projection and the respective first wall.
With this structure, a gradually curving outer configuration is provided at the connection between the base end of each projection and the corresponding first wall. Therefore, even when a force is applied to the tip end of each projection and the base end is subjected to a bending stress, it is possible to prevent a stress concentration on a particular portion of the base end. Accordingly, even when a pulling force (a force to pull out the light source or the photodetector from the corresponding receiving portion through the opening) is generated and each of the projection is pressed by the light source or the photodetector, it is possible to prevent the projection from easily breaking. Thus, the light source and the photodetector can be reliably fixed.
Preferably, each of the light source and the photodetector may include a bottom surface facing the opening of the respective receiving portion and a side surface facing the respective first wall, and the tip end of each projection may include a first surface and a second surface for engagement with the bottom surface and the side surface, respectively.
With this structure, since the second surface of each projection engages the side surface of the light source or the photodetector, the projection is prevented from rotating in a direction in which the second surface faces toward the side surface of the light source or the photodetector. Therefore, even when a pulling force is exerted on the light source or the photodetector which, as a result, presses the first surface of the corresponding projection toward the opening of the corresponding receiving portion, it is possible to prevent the projection from easily rotating in that direction. Thus, fixing of the light source and the photodetector becomes more reliable.
Preferably, each projection may be connected to the respective first wall at a portion away from a longitudinal end edge of the respective slit, and the projection is wider than the slit.
With this structure, even in the case where each slit needs to be narrowed to enhance the detection ability of the photointerrupter, the projection can be made wider than the slit to have a sufficient strength.
Preferably, the light source may comprise a light emitting element sealed in a resin, and a plurality of leads projecting from the resin in electrical connection with the light emitting element.
Preferably, the photodetector may comprise a light receiving element sealed in a resin, and a plurality of leads projecting from the resin in electrical connection with the light receiving element.
In accordance with a second aspect of the present invention, there is provided a case for a photointerrupter comprising a pair of receiving portions each of which is open at one end, a plurality of walls defining the pair of receiving portions. The plurality of walls of the case include a pair of first walls each of which is formed with a respective elongated slit. The case further includes a pair of projections each of which projects into a respective one of the receiving portions for preventing the light source or the photodetector accommodated in the respective receiving portion from coming out of the receiving portion. Each projection is connected to the respective first wall on an extension line of the respective slit.
The case of the photointerrupter having the above-described structure can obtain the same advantages as those obtained by the photointerrupter provided in accordance with the first aspect of the present invention.
Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings.